With Ikeda-san

We set up the same mirror mount as the STM inside the IFI chamber and started the measurement, but no significant peak was observed around 120 Hz. Further details will be reported later.

> According to klog 18501, the actual IFI STM mirror is a 2-inch mirror with a thickness of 11 mm. 

According to the drawing, the minimum mirror thickness that can be held by the pawls is 11.1 mm.
If the mirror is secured only by the pawls, there is a possibility that it may be slightly loose.
https://www.newport.com/medias/sys_master/images/images/h87/h46/8997797691422/8822-AC-UHV-RC.pdf

With Ikeda-san

We examined the new mirror mount (8822-AC-UHV). It appears that there are two possible ways to secure a mirror in this mount:

1. Using the spring-loaded pawls at the back of the mirror.
2. Using a 5/64 screw on the side of the mount.

The spring-loaded pawls are a unique mechanism that is not commonly seen in other mounts. These components, possibly made of PEEK, press the mirror from the back. Each pawl has a small bolt, but the pawl can be lifted and rotated without turning this bolt, allowing for easy retraction when inserting the mirror.
According to the manufacturer’s webpage:
"Spring-loaded pawls gently, but securely, hold a high-precision 2-inch (50.8 mm) diameter optic from the back against three points on the front plate of the mount."
This suggests that securing the mirror solely with the pawls is also a viable option. A conceptual diagram of the pawl mechanism is attached, illustrating my interpretation of its structure.

The actual method used to fix IFI STM mirrors inside the IFI chamber is unknown. To investigate, we performed vibration measurements under different fixation methods. The mirrors used in this test were the same as those from the previous measurement.
According to klog 18501, the actual IFI STM mirror is a 2-inch mirror with a thickness of 11 mm. The thickness of the mirror used in this test has not yet been verified.

Measurement Setup

The mirror mount was attached to the POS table using a pedestal post secured in three directions. We conducted vibration measurements under four different fixation methods:

1. Side screw + three rear pawls
2. Side screw only
3. Side screw + three rear pawls (with one pawl screw pushed in by ~1.3 mm to mimic the actual STM2 fixation method)
4. Three rear pawls only (with one pawl screw pushed in by ~1.3 mm to mimic the actual STM2 fixation method)

For each fixation method, we took two types of measurements:

• "Free" measurement (no external excitation)
• "Shake" measurement (lightly tapping the pedestal post from the back)

We plan to conduct additional measurements with different fixation methods in the future.

Results

No significant peak near 120 Hz was observed, and no major differences were found between the different fixation methods. However, minor differences around 600 Hz may exist.
The attached graph overlays all measurement results, using the side screw + rear pawl fixation method as the reference, which is assumed to be the standard fixation method..

Pictures

With Hido-san,

We investigated how resonance changes depending on different methods of fixing mirror.

We found that the mirrors we had been using were 12 mm thick, so we installed and measured 11 mm thick mirror as well.

As a result, no resonance was observed around 120 Hz, and probably none around 220 Hz either (details to be provided later). A significant resonance was observed at 270 Hz. Upon investigation, we suspect that this resonance may be due to the "neck" of the pedestal.

A detailed report will follow.

With Hido-san

Objective

The objective of this experiment was to complete the remaining measurements from the previous day and evaluate a newly identified mirror that matches the one inside the IFI chamber. Specifically, the focus was on determining whether different fixation methods affect the resonance frequency, checking for peaks around 120Hz and 220Hz, and investigating the cause of the prominent peak observed at 270Hz.

Procedure

1. Measurements with Variations

• Conducted measurements under different conditions:
  • With and without shaking.
  • With shaking of the laser source.
  • With the side screw released or tightened.
  • With the pawls in different configurations:
    • Released.
    • Restored to the original position.
    • Fully tightened.
    • Adjusted to simulate the IFI chamber conditions.

Results and Considerations

• No significant changes were observed regardless of the fixation method, indicating that the 120Hz and 220Hz noise sources are likely unrelated to the mirror mounting configurations.

2. Investigation of 270Hz Resonance

• Applied force using a wrench to assess its effect on resonance behavior.
• Inserted a washer between the mirror holder and the mount to study its influence on resonance characteristics.
• Attached the mirror mount on a thin post and conducted measurements.

Results and Considerations

• The 270Hz peak remained unchanged when force was applied to the thick pedestal, and it disappeared when the mirror was mounted on a thin pole, suggesting that the source of resonance is neither the pedestal itself nor the mirror mount.
• Introducing a washer between the mirror mount and the pedestal caused some variation in the peak, leading to the hypothesis that the neck of the pedestal might be the primary source of the 270Hz resonance.

3. Testing Different Mirror Mount Configurations

• Initially, measurements were conducted using a 12mm mirror.
• Later, an 11mm mirror(link), identical to the one inside the IFI chamber, was found and tested under the same conditions.
• The PYD-20 mirror was examined but not measured due to its significantly different thickness.
• Adjusted the mirror’s positioning to simulate IFI chamber conditions.

4. Thickness Measurements

• Measured the thickness of the 12mm and 11mm mirrors.
• The PYD-20 mirror was inspected but not measured.

Conclusion

The various configurations and shaking tests were performed to assess the mechanical stability and potential contributions to noise. The analysis of the collected data showed no peaks around 120Hz and 220Hz. The prominent peak observed at 270Hz is likely due to the resonance of the pedestal’s neck region.

Legend for Attached Graphs

• "Back: locked(+1.9mm)": Indicates that the back pawls' screws were adjusted to protrude 1.9mm from the front.
• "Back: locked(only one pawl)": Denotes a condition where only one of the three back pawls was locked while the other two were released, meaning the mirror was held in a very loose state.

As there are too many graphs, I picked up the data in the case of 11mm thickness mirror and related graphs.

Pictures: link

Slides used in a commissioning meeting for this topic: JGW-T2516543

With Kenta Tanaka

We first attempted to reproduce the same conditions as last week and conducted measurements. As a result, a peak appeared at 120 Hz. The cause of this peak is unknown, but it persisted even after changing the mirror mounting method. Electrical noise is also a possible factor.

To investigate further, we inserted a small optical breadboard plate (MB1515/M) under the pedestal. We then placed the pedestal at the edge of the plate and performed measurements. A broad peak noise around 120 Hz was observed, which varied depending on the mounting method (using two clamps) and the amount of overhang.

In the final measurement, we kept the clamping method as consistent as possible and only varied the overhang. As a result, the peak frequency changed.

Graphs:

• First graph: The 120 Hz peak observed under the same conditions as last week, without the plate.
• Second graph: The difference in the final measurement results. A comparison between cases where the overhang was 4.6 mm and 6.3 mm.

Detailed data will be reported later.
The POS table has been neatly cleaned up. All measurement equipment, mounts, and so on have been brought back to the office, making it possible to conduct additional tests at Toyama University or other locations if needed.